Data/hora: 09/06/2024 13:57:06

Provedor de dados: | 5
País: | France
Título: | Réseau trophique de l'anse de l'Aiguillon : dynamique et structure spatiale de la macrofaune et des limicoles hivernants
Autores: | Degre, Delphine.
Data: | 2006-09-26
Ano: | 2006
Palavras-chave: | Carrying capacity; Inverse analysis; Spatio temporal patterns; Food web; Isotope; Waders; Molluscs bivalves; Aiguillon Cove; Capacité d'accueil; Analyse inverse; Dynamique des populations; Structure spatiale; Réseau trophique; Isotope; Limicoles; Bivalves; Mollusques; Anse de l'Aiguillon.
Resumo: | The Aiguillon Cove has been preserved as Natural Reserves since 1996 and 1999 for its international importance as wintering areas for waterbirds. The benthic communities of this a macrotidal bay were still little studied. In order to understand the spatial pattern and the dynamics of the main compartments of its trophic network, two cartographies were carried out at the time of the departure (March) and the arrival (October) of the waders. A monthly study was carried out too in three stations of the upper mudflat. The spatio-temporal homogeneity of the granulometry of the sediments and the strong seasonal variation of the salinity of pore water were highlighted. The molluscs' diversity is low, especially on the upper mudflat where abundance of Hydrobia ulvae and biomass of Scrobicularia plana dominate. Various facies of the "Macoma balthica ¿ community" are present according to hypsometry, the average diameter of the sediments and salinity. The total mollusc stock exceeds 11.000 tons of fresh mass with shell for the 37,45 km ² of the cove. Approximately 3% of this stock constitutes the available ash free dry mass, represented by 62 to 83% of S. plana. The ingestible and profitable ash free dry mass ash for short bill waders reached 48 tons in March and 105 tons in October. 27% of the bivalves' biomasses are accessible to short bill waders and 97% to long bill waders. The long-lived bivalves, S. plana and M. balthica have a turnover time from 1 to 5 years, while Abra tenuis renews its populations in 5 months. The recruitments spread out over the year for S. plana and over spring for M. balthica and A. tenuis. But bivalves' population undergone strong eliminations partly related to the waders predation. The waders wintering on the Aiguillon Cove reach 41.000 individuals, including 57% of Dunlins, which, with Black-tailed Godwits, Knots and Avocets, are more numerous than the international importance threshold. The phenology of their migrations is complex with successive or simultaneous movements of various subspecies. The spatial distribution of these 4 species during low tide is significantly correlated with the average diameter of the sediments and the salinity of pore water because of preferential food activity along the channels. It shows a high seasonal and interannual variability and a covering of niches between Avocets and Godwits and between Dunlins and all the other species. The total consumption of benthivorous waterbirds is estimated to 150-799 T.y-1, including 30 % by the Common Shelduck, 43 % by short bill waders and 27 % by long bill waders. To sustain this consumption, the molluscs must product 2-13 g.m-².an-1 that is lower than the secondary production of all bivalves. Moreover, the waders' feeding is much diversified. The carrying capacity of the study site is not reached in term of food resources. By stable isotope analysis of the contour feathers, rectrices and blood of waders, we confirmed their mainly benthivorous feeding both during the wintering and during the moult. The strong inter-individual variance of the &amp;#948;13C and the &amp;#948;15N of the various waders' species point out that food strategies are more individual than specific with a preference more or less marked for polychaetes or bivalves adults, whose flesh are enriched in 15N than those of the youthful ones. By inverse analysis, we estimate the seasonal carbon flows on an average 1 m ² of intertidal mudflat. The bentho-pelagic food-web is dominated by detrital activity. Flows are sensitive to the microphytobenthos or detritus resuspension and to the bivalves' productivity. The activity of waders is weak, contrary to that of fish, and seems to be not limited by the macrofauna biomass. Lastly, the indices of network analysis showed that the system is not very complex, little mast, very productive and net exporter of quality.
Tipo: | Text
Idioma: | Francês

Identificador:

http://archimer.ifremer.fr/doc/2006/these-2097.pdf

http://archimer.ifremer.fr/doc/2006/sup-2097.pdf

Editor: | Université de la Rochelle
Relação: | http://archimer.ifremer.fr/doc/00000/2097/
Formato: | application/pdf